Lattice dynamics and electronic structures of Ti3C2O2 and Mo2TiC2O2 (MXenes): The effect of Mo substitution

Abstract

Recently, Mo2TiC2, an ordered two transition metals MXene has been synthesized, which offers a great opportunity to explore the effect of transition metal in MXenes. Here, the structure, dynamical and electronic properties of Mo2TiC2O2 and Ti3C2O2 are compared to investigate the effect of Mo substitution. Our density functional calculations predict that Mo2TiC2O2 prefer different structural configuration than the well-known Ti3C2O2. By comparing the dynamics and electronic structure between Mo2TiC2O2 and Ti3C2O2, we found that the replacement of Ti with Mo could enhance the chemical bonding and the electronic coupling of oxygen and carbon with metals. In addition, the GGA calculations show that Mo could change metallic Ti3C2O2 into semiconducting Mo2TiC2O2, which agrees with the recently experimental observation. Our calculations also show that spin-orbit coupling (SOC) effect is important to the electronic band structure of Mo2TiC2O2. The SOC could split the degenerate d bands on the Fermi level and the band inversion that is significant to the nontrivial band topology is found in Mo2TiC2O2. Our results indicate that Mo2TiC2O2 may be a two-dimensional topological (2D TI) semiconductor with band gap (HSE06+SOC) of 0.17eV.